1. Field of the Invention
The present invention relates to a driving mechanism for rotating a roller closely contacting a photo-receptor web in a printer, and, more particularly, to a roller driving mechanism and process for transferring rotational power between the roller and a motor in an image formation apparatus.
2. Description of the Related Art
Various types of structures connecting a gear to a roller to feed a photo-receptor web are used in printers. A common design for image formation equipment such as a printer or a photocopier for printing images and characters onto printable paper uses a photo-receptor web supported by and wound around a pair of rollers, a laser scanning unit that forms electrostatic latent images or characters on the surface of the photo-receptor web, and a developing unit that forms toner images corresponding to the electrostatic latent images on the photo-receptor web. The toner images formed on the photo-receptor web are transferred to printable paper stock via a transfer roller while the photo-receptor web passes between set of rollers. Typically, gears transfer rotational power from a motor to the rollers. We have found that conventional structures for connecting the gear to the roller are not suitable to transfer the rotating power to the roller precisely. If a load is applied to the roller, the gear can not rotate the roller precisely because the load applied to the roller causes the structure between the roller and the gear to prevent the gear from transferring the rotating power to the roller precisely.
We have noticed that it is not easy during assembly or during subsequent operation of the roller driving apparatus to precisely perform the installation and the engagement of thread portions which are formed on first and second clutch members and which face each other. Moreover, it takes too much time for assembly, maintenance and repair of the roller driving apparatus since the entire structures are complicated. Furthermore, the first and second clutch members and neither engage each other precisely nor rotate integrally, thereby the rotating force of the motor is not accurately transferred to the roller because one clutch member retreats from the other clutch member when a load is applied to the roller. The rotating power transferred from motor to one of the clutch members and the load transferred from supporting shaft to the other of the clutch member causes the two clutch members to retreat from each other against the elastic force of the spring. Therefore, one of the clutch members slips from the other clutch member, and the rotational force of the motor is not accurately transferred to the roller. Therefore, constant-speed rotation of the roller and constant speed circulation of the photo-receptor are not achieved. The level of quality in the printing operation is lowered. In our opinion, this design for the roller driving mechanism for rotating the rollers that contact and circulate the photo-receptor web is neither suitable to transfer the rotating force from the motor to the rollers nor adequate to assemble and maintain the clutch members to contact each other precisely.